Abstract:

ABSTRACT Chromatic acclimation (CA) provides many cyanobacteria with the ability to tailor the properties of their lightharvesting
antennae to the spectral distribution of ambient light. CA was originally discovered as a result of its dramatic
cellular phenotype in red and green light. However, discoveries over the past decade have revealed that many pairs of light
colors, ranging from blue to infrared, can trigger CA responses. The capacity to undergo CA is widespread geographically,
occurs in most habitats around the world, and is found within all major cyanobacterial groups. In addition, many other
cellular activities have been found to be under CA control, resulting in distinct physiological and morphological states for
cells under different light-color conditions. Several types of CA appear to be the result of convergent evolution, where
different strategies are used to achieve the final goal of optimizing light-harvesting antenna composition to maximize
photon capture. The regulation of CA has been found to occur primarily at the level of RNA abundance. The CA-regulatory
pathways uncovered thus far are two-component systems that use phytochrome-class photoreceptors with sensor-kinase
domains to control response regulators that function as transcription factors. However, there is also at least one CAregulatory
pathway that operates at the post-transcriptional level. It is becoming increasingly clear that large numbers
of cyanobacterial species have the capacity to acclimate to a wide variety of light colors through the use of a range of
different CA processes.